In hydraulic circuits which contain moving fluids, it is frequently necessary to eliminate gas bubbles before they reach functional parts. A specialized example of such a circuit is a cardio-pulmonary bypass circuit employed during open-heart procedures. If blood in such a circuit contains air or gas emboli, it is imperative to remove such emboli (i.e. bubbles) before they reach the patient. Otherwise, the emboli may cause serious neurological damage or death. Blood-separating devices in cardio-pulmonary circuits are usually placed between the arterial pump and the patient so that air emboli are removed before the blood reaches the patient. Many surgical teams use arterial filters to serve as a bubble trap. The filter does not allow bubbles to pass through the tiny filter openings. The problem is that the openings must be very small to be effective bubble stops, and such small openings may cause harm to the delicate red blood cells. There is, thus, a need for a phase-separating device which passes blood atraumatically and separates air. The air may be separated and returned to the oxygenator to recover any physiological liquids delivered therewith. Similar problems exist with other physiological fluids which may be found in the operating field.
There are several bubble traps presently available. One has a large internal volume, and thus wastes a great deal of blood, and it has to be disassembled and cleaned after every operation because it is not a disposable device. Another device is made from polymer composition material and is pre-sterilized and disposable. This device separates bubbles from the blood by relying on circular flow, but the problem is that there are internal flow-directing vanes which present a large surface area. The edges of the vanes may cause trauma to red blood cells as they impinge upon the vanes during flow. Furthermore, the large surface area may be harmful because it is known that any surface contact with blood may cause platelet damage. Thus, it is desirable to minimize the surface area in contact with the flowing blood.
Another commercially available separator is made of polymer material and is disposable. It relies on circular flow, and to achieve this flow, the blood inlet fitting is tangentially directed. The inlet is a side fitting positioned in the horizontal plane, and the attachment of tubing thereto becomes difficult because in normal circumstances, the tubing will hang and may pinch. The tubing does not drape naturally from such a side fitting.
Examples of two prior bubble trap structures are found in George G. Siposs U.S. Pat. Nos. 4,344,777 and 4,368,118.
There is need for a simple, disposable device which can be inexpensively produced and pre-sterilized. Such a device needs to separate gas bubbles from a moving stream of physiological liquid, such as blood, without being unnecessarily complex. Furthermore, the device must have a minimum blood contact surface and must have no structure inside the device with which the flowing liquid would be in contact which could cause trauma to the delicate blood cells. In addition, the device must have a minimum interior volume to minimize blood loss. Also, the device must have a minimum number of easy-to-produce parts to be trouble-free and inexpensive.